Migration Assistant won't connect

Hi;
I am trying to migrate from Windows XP to Mac Lion (10.7).
I run the Migration Assistant on the Mac, then go to the Windows PC where I installed the software, but the Windows PC reports an error. Cannot find any other computers.

I know that both computers have network connectivity. I am able to drag and drop files from one to the other.
I just thought that using Migration Assistant would make life easier.